1. Field of the Invention
The present invention relates to a method and apparatus for video conferencing applications such as distance learning. More particularly, it relates to a method and apparatus involving a multi-cast server for multi-point data transmission for multi-party video conferencing.
2. Description of the Prior Art
Video conferencing promises to bring people in far-flung communities together through communication networks. Distance learning expands video conferencing usage by allowing students in small communities to attend courses taught by experts, without having to travel to major educational institutions.
Prior art distance learning systems consisted of classrooms equipped with video cameras, large screen video monitors, local video and audio mixing facilities, and a means to transmit video and audio information between these sites. During a distance learning session, one such classroom is designated as the teacher site; other sites participate in the distance learning session as student classrooms. Early distance learning systems employed analog video equipment, and recently digitally encoded video, which is carried over dedicated data links. A typical arrangement includes: point-of-presence video codecs, a multi-conference control unit (MCU) that switches video between different sources, and dedicated point-to-point data links connecting the point-of-presence codecs with the MCU. A distributed conference-control application manages the class schedules and source switching.
There are several drawbacks of MCU based distance learning system configurations that stem from the star-topology and dedicated links of the system. The first drawback is dedicated transmission: all video streams must be transmitted to the MCU before they reach participants in a video conferencing or distance learning session. This means that bandwidth must be dedicated for all participants to transmit their audiovisual stream, even if they are not being viewed by other participants. Since all incoming and outgoing video data is transmitted on point-to-point links, bandwidth is wasted in the network that could otherwise be used for non-video data transmissions. The second drawback is that of centralized resource bottleneck. A traditional MCU video source switching can become a bottleneck in the system, especially when there are concurrent distance learning sessions. The third drawback is that expansion of the monolithic multi-conferencing unit is difficult. The complexity of the MCU increases with each distant site that is added. A traditional MCU serves all video conference sessions in a particular network. Since the capacity of the MCU is fixed, as the network expands, the MCU has to be expanded to accommodate the increased number of users. An MCU has limitations on the total number of ports that can be served at one time. As a result, a major increase in capacity requires replacement of the MCU.
These unresolved problems and deficiencies are clearly felt in the art and are solved by the invention in the manner described below.